Effects of a Surfactant on the Electrocatalytic Activity of Cobalt Hexacyanoferrate Modified Glassy Carbon Electrode Towards the Oxidation of Dopamine

The cobalt hexacyanoferrate film (CoHCF) was deposited on the surface of a glassy carbon (GC) electrode with a potential cycling procedure in the presence and absence of the cationic surfactant, cetyl trimethylammonium bromide (CTAB), to form CoHCF modified GC (CoHCF/GC) electrode. It was found that CTAB would affect the growth of the CoHCF film, the electrochemical behavior of the CoHCF film and the electrocatalytic activity of the CoHCF/GC electrode towards the electrochemical oxidation of dopamine (DA). The reasons of the electrochemical behavior of CoHCF/GC electrode influenced by CTAB were investigated using FTIR and scanning electron microscope (SEM) techniques. The apparent rate constant of electrocatalytic oxidation of DA catalyzed by CoHCF was determined using the rotating disk electrode measurements.     

新法制备铁氰化钴修饰玻碳电极及多巴胺的电催化氧化

新法制备铁氰化钴修饰玻碳电极及多巴胺的电催化氧化     

Electrochemistry and electrocatalytic activity of catechin film on a glassy carbon electrode toward the oxidation of hydrazine

A very stable electroactive film of catechin was electrochemically deposited on the surface of activated glassy carbon electrode. The electrochemical behavior of catechin modified glassy carbon electrode (CMGCE) was extensively studied using cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and the stability of the deposited film were examined. The charge transfer coefficient (α) and charge transfer rate constant (k _s) for catechin deposited film were calculated. It was found that the modified electrode exhibited excellent electrocatalytic activity toward hydrazine oxidation and it also showed a very large decrease in the overpotential for the oxidation of hydrazine. The CMGCE was employed to study electrocatalytic oxidation of hydrazine using cyclic voltammetry, rotating disk voltammetry, chronoamperometry, amperometry and square-wave voltammetry as diagnostic techniques. The catalytic rate constant of the modified electrode for the oxidation of hydrazine was determined by cyclic voltammetry, chronoamperometry and rotating disk voltammetry and was found to be around 10⁻³ cm s⁻¹ . In the used different voltammetric methods, the plot of the electrocatalytic current versus hydrazine concentration is constituted of two linear segments with different ranges of hydrazine concentration. Furthermore, amperometry in stirred solution exhibits a detection limit of 0.165 μM and the precision of 4.7% for replicate measurements of 40.0 μM solution of hydrazine.     

Electrochemical oxidation and determination of ceftriaxone on a glassy carbon and carbon-nanotube-modified glassy carbon electrodes

The electrochemical behavior of ceftriaxone was investigated on a carbon-nanotube-modified glassy carbon (GC-CNT) electrode in a phosphate buffer solution, pH = 7.40, and the results were compared with those obtained using the unmodified one [glassy carbon (GC) electrode]. During oxidation of ceftriaxone, an irreversible anodic peak appeared, using both modified and unmodified electrodes. Cyclic voltammetric studies indicated that the oxidation process is irreversible and diffusion-controlled. The number of electrons exchanged in the electrooxidation process was obtained, and the data indicated that ceftriaxone is oxidized via a one-electron step. The results revealed that carbon nanotube promotes the rate of oxidation by increasing the peak current. In addition, ceftriaxone was oxidized at lower potentials, which thermodynamically is more favorable. These results were confirmed by impedance measurements. The electron-transfer coefficients and heterogeneous electron-transfer rate constants for ceftriaxone were reported using both the GC and GC-CNT electrodes. Furthermore, the diffusion coefficient of ceftriaxone was found to be 2.74 × 10⁻⁶ cm² s⁻¹. Binding of ceftriaxone to human serum albumin forms a kind of electroreactive species. The percentage of interaction of ceftriaxone with protein was also addressed. A sensitive, simple, and time-saving differential-pulse voltammetric procedure was developed for the analysis of ceftriaxone, using the GC-CNT electrode. Ceftriaxone can be determined with a detection limit of 4.03 × 10⁻⁶ M with the proposed method.     

Palladium nanoparticle decorated carbon ionic liquid electrode for highly efficient electrocatalytic oxidation and determination of hydrazine

In this work arrays of palladium nanoparticles were synthesized on carbon ionic liquid electrode (CILE) (Pd/CILE), and the electrocatalytic oxidation of hydrazine was investigated using this electrode. Electrochemical oxidation of hydrazine in phosphate buffer (pH 7) was performed using cyclic voltammetry and square wave voltammetric techniques (SWV). Using the proposed electrode, a highly reproducible and well-defined peak was obtained for hydrazine at a very low potential of −0.02 V versus Ag/AgCl. A linear dynamic range of 5-800 μM with an experimental detection limit of 0.82 μM was obtained. These results show that the proposed electrode displays better electrocatalytic activity compared to the previously reported palladium modified electrodes towards oxidation of hydrazine.     

Caffeic acid modified glassy carbon electrode for electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH)

A new modified electrode was prepared by electrodeposition of caffeic acid (CFA) at the surface of an activated glassy carbon electrode. Cyclic voltammetry was used to investigate the redox properties of this electrode at various solution pH values and at various scan rates. The pH dependence of the electrode response was found to be 58.5 mV/pH, which is very close to the expected Nernstian value. The electrode was also employed to study electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH), using cyclic voltammetry, chronoamperometry and rotating disk voltammetry as diagnostic techniques. It was found that the modified electrode exhibits potent and persistent electrocatalytic properties toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 450 mV compared to the process at an unmodified electrode. The electrocatalytic current increases linearly with NADH concentration in the range tested from 0.05 to 1.0 mM. The apparent charge transfer rate constant and transfer coefficient for electron transfer between the electrode surface and immobilized CFA were calculated as 11.2 s⁻¹ and 0.43, respectively. The heterogeneous rate constant for oxidation of NADH at the CFA-modified electrode surface was also determined and found to be about 3 × 10³ M⁻¹ s⁻¹. Finally, the diffusion coefficient of NADH was calculated as 3.24 × 10⁻⁶ cm² s⁻¹ for the experimental conditions, using chronoamperometric results. Received: 6 January 1999 / Accepted: 11 May 1999     

An amperometric sensor for hydrazine based on nano-copper oxide modified electrode

A sensitive hydrazine sensor has been fabricated using copper oxide nanoparticles modified glassy carbon electrode (GCE) to form nano-copper oxide/GCE. The nano-copper oxide was electrodeposited on the surface of GCE in CuCl₂ solution at −0.4 V and was characterized by Scanning electron microscopy and X-ray diffraction. The prepared modified electrode showed a good electrocatalytic activity toward oxidation of hydrazine. The electrochemical behavior of hydrazine on nano-copper oxide/GCE was explored. The oxidative current increased linearly with improving concentration of hydrazine on nano-copper oxide/GCE from 0.1 to 600 μM and detection limit for hydrazine was evaluated to be 0.03 μM at a signal-to-noise ratio of 3. The oxidation mechanism of hydrazine on the nano-copper oxide/GCE was also discussed. The fabricated sensor could be used to determine hydrazine in real water.     

Sensitive voltammetric determination of 2-mercaptobenzimidazole at electropolymerized nickel and copper tetraaminophthalocyanine membrane modified electrode

The voltammetric determination of 2-mercaptobenzimidazole (MBI) was studied by using a glassy carbon electrode (GCE) coated with polymeric nickel and copper tetraaminophthalocyanine (poly-NiTAPc and poly-CuTAPc) membrane. The polymeric membrane decreases the overpotential of oxidation of MBI by 136.2 and 115.0 mV and increases the oxidation peak current by about 3.4 and 3.3 times, while the reduction peak potential shifts positively by 113.0 and 84.1 mV and the peak current increases by about 10 and 7 times in 0.1 mol·l⁻¹ phosphate buffer solution (PBS) at pH = 2.0 for poly-NiTAPc and poly-CuTAPc, respectively, compared to the unmodified GCE. The results indicated that the developed electrode exhibited efficient electrocatalytic activity for MBI with relatively high sensitivity, stability, and long life. The oxidation and reduction peak currents of MBI were linear to its concentrations ranging from 8.0 × 10⁻⁵ to 1.0 × 10⁻³ mol·l⁻¹ at poly-NiTAPc and from 2.0 × 10⁻⁵ to 1.0 × 10⁻³ mol·l⁻¹ at poly-NiTAPc membranes modified electrodes, respectively, with a low limit of detection.     

Electrochemical,microscopic, and EQCM studies of cathodic electrodeposition of ZnO/FAD and anodic polymerization of FAD films modified electrodes and their electrocatalytic properties

Two kinds of chemically modified electrodes were prepared. In the first type of electrodes, zinc oxide (ZnO) and flavin adenine dinucleotide (FAD) molecules were deposited onto the glassy carbon-, gold-, and SnO₂-coated glass electrodes by using cyclic voltammetry from the bath solution containing aqueous 0.1 M zinc nitrate, 0.1 M sodium nitrate, and 1 × 10⁻⁴ M FAD. It was called as ZnO/FAD modified electrodes. The second type of modified electrode was prepared by the electropolymerization method. Electrochemical polymerization of FAD was carried out from the acidic solution containing 1 × 10⁻⁴ M FAD monomers onto electrode surfaces. This poly(FAD)-modified electrode yields a new redox couple in addition to the monomers redox couple. The influence of the concentrations, pH, and electrocatalytic properties of the ZnO/FAD- and poly(FAD)-modified electrodes are investigated by means of the in situ technique electrochemical quartz–crystal microgravimetry (EQCM) combined with cyclic voltammetry and the ex situ technique scanning electron microscopy. From these studies, it appears that the cathodic deposition of ZnO/FAD-modified electrodes gives only one redox couple, and the anodically polymerized FAD film-modified electrodes gives two reversible redox couples. The pH dependence of the redox responses were investigated and the kinetics of electron transfer was evaluated. In addition, the EQCM technique was employed to follow the deposition process of both kinds of modified electrodes in real time as well as the characteristics of the charge transfer associated with the surface-confined redox-active couples. The electrocatalytic activity of the poly(FAD)-modified electrode towards the reduction of hydrogen peroxide and the oxidation of dopamine and ascorbic acid was explored. The important electrocatalytic properties of poly(FAD)-modified electrode were observed for simultaneous separation of dopamine and ascorbic acid in neutral solution. This poly(FAD)-modified electrode has several advantages than the previously reported FAD-modified electrodes.     

Surface modification of amine-functionalised graphite for preparation of cobalt hexacyanoferrate (CoHCF)-modified electrode: an amperometric sensor for determination of butylated hydroxyanisole (BHA)

A cobalt hexacyanoferrate (CoHCF)-modified graphite paraffin wax composite electrode was prepared by a new approach. An amine-functionalised graphite powder was used for the fabrication of the electrode. A functionalised graphite paraffin wax composite electrode was prepared and the surface of the electrode was modified with a thin film of CoHCF. Various parameters that influence the electrochemical behaviour of the modified electrode were studied by varying the background electrolytes, scan rates and pH. The modified electrode showed good electrocatalytic activity towards the oxidation of butylated hydroxyanisole (BHA) under optimal conditions and showed a linear response over the range from 7.9 × 10⁻⁷ to 1.9 × 10⁻⁴ M of BHA with a correlation coefficient of 0.9988. The limit of detection was 1.9 × 10⁻⁷ M. Electrocatalytic oxidation of BHA was effective at the modified electrode at a significantly reduced potential and at a broader pH range. The utility of the modified electrode as an amperometric sensor for the determination of BHA in flow systems was evaluated by carrying out hydrodynamic and chronoamperometric experiments. The modified electrode showed very good stability and a longer shelf life. The modified electrode was applied for the determination of BHA in spiked samples of chewing gum and edible sunflower oil. The advantage of this method is the ease of electrode fabrication, good stability, longer shelf life, low cost and its diverse application for BHA determination. Figure Cyclic Voltammogram of () CoHCF modified electrode, () in presence of 1.9 x 10⁻⁵ M of BHA and () bare electrode, () in the presence of 1.9 x 10⁻⁵ M of BHA in 1.0 M NaCl, pH 7.0     

芦丁碳纳米管修饰玻碳电极电催化氧化肼的研究

应用循环伏安法研究了芦丁碳纳米管修饰玻碳电极(Rt-MWNT/GC)的电化学行为及其对肼的电催化氧化.实验表明,该修饰电极能使肼的氧化电位降至260 mV附近,表现出良好的电催化作用.安培法测得催化电流与肼浓度在2.5×10-6～1.0×10-4 mol·L-1范围内呈线性关系,检出限5×10-7 mol.L-1.     

Carbon nanotubes/alizarin red S–poly(vinylferrocene) modified glassy carbon electrode for selective determination of dopamine in the presence of ascorbic acid

A modified electrode was fabricated by electrochemical formation of poly(vinylferrocene) on the multi-wall carbon nanotube-alizarin red S matrix covered glassy carbon electrode. A higher electrochemical activity was obtained to the electrocatalytic oxidation of dopamine. The electrode surface was characterized electrochemically and spectroscopically. Poly(vinylferrocene) (PVF) in electrode was used as an electron transfer mediator in the electrochemical oxidation of compounds due to its perfect reversible redox properties. Multi-wall carbon nanotubes (MWCNTs) / alizarin red S (ARS)–PVF electrode was used to the determination of dopamine in the presence of ascorbic acid in 0.1 M sulphate buffer solution at pH 7. The performance of the MWCNTs/ARS–PVF electrode was evaluated by DPV and amperometry.     

Magnetic field effects on microstructural variation of electrodeposited cobalt films

The electrodeposition process of Co films in a sulfuric acid solution was examined in a magnetic field (0–5 T). The surface morphology of Co films electrodeposited without a magnetic field was drastically modified with the variation of hydrogen gas evolution rate. Crystalline α-Co was formed in the range of pH = 1.5–6.0, while β-Co was not observed. When the magnetic field was superimposed perpendicular to the electric field in the acidic solution (pH = 1.5), the hydrogen evolution rate was promoted by MHD convection, which enhanced the ionic mass transfer (H⁺ and Co²⁺) near the electrode surface. Moreover, crystalline β-Co was formed simultaneously with the appearance of the elongated ridge-shape precipitates under a higher magnetic field (≥3 T). Contribution to special issue “Magnetic field effects in Electrochemistry”     

Electrocatalytic oxidation of quinine sulfate at a multiwall carbon nanotubes-ionic liquid modified glassy carbon electrode and its electrochemical determination

The electrocatalytic oxidation of quinine sulfate (QS) was investigated at a glassy carbon electrode, modified by a gel containing multiwall carbon nanotubes (MWCNTs) and room-temperature ionic liquid of 1-Butyl-3-methylimidazolium hexafluorophate (BMIMPF₆) in 0.10 M of phosphate buffer solution (PBS, pH 6.8). It was found that an irreversible anodic oxidation peak of QS with E _pa as 0.99 V appeared at MWCNTs-RTIL/glassy carbon electrode (GCE). The electrode reaction process was a diffusion-controlled one and the electrochemical oxidation involved two electrons transferring and two protons participation. Furthermore, the charge-transfer coefficient (α), diffusion coefficient (D), and electrode reaction rate constant (k _f) of QS were found to be 0.87, 7.89 × 10⁻³ cm²⋅s⁻¹ and 3.43 × 10⁻² s⁻¹, respectively. Under optimized conditions, linear calibration curves were obtained over the QS concentration range 3.0 × 10⁻⁶ to 1.0 × 10⁻⁴ M by square wave voltammetry, and the detection limit was found to be 0.44 μM based on the signal-to-noise ratio of 3. In addition, the novel MWCNTs-RTIL/GCE was characterized by the electrochemical impedance spectroscopy and the proposed method has been successfully applied in the electrochemical quantitative determination of quinine content in commercial injection samples and the determination results could meet the requirement.     

Characterization of PVC-Tetraruthenated Metalloporphyrins Modified Electrodes: Application as Electrocatalyst in the Nitrite Reduction

Summary: This paper describes the electrochemical reduction of nitrite ion in 0.1 M NaClO₄, on glassy carbon or ITO electrodes modified with mixtures PVC- tetraruthenated metalloporphyrins. This electrode is able to keep the extraordinary electrocatalytic properties of the macrocycle allowing multielectronic transfers and a great stability as a consequence of the inclusion of the macrocycles into a polymeric support such as PVC. On the other hand, the electrochemical reduction of nitrite ion on these modified electrodes studied by cyclic voltammetry shows an enhancement in the current values and lower overpotential compared with the activity of the bare glassy carbon electrode. Controlled potential electrolysis experiments verify the production of ammonia, hydrazine and hydroxylamine, showing the electrocatalytic character and the stability of this modified electrode.     

Glassy carbon electrodes modified by multiwalled carbon nanotubes and poly(neutral red): A comparative study of different brands and application to electrocatalytic ascorbate determination

The electrochemical behaviour of glassy carbon electrodes coated with multiwalled carbon nanotubes (MWCNT) from three different sources and with different loadings has been compared, with a view to sensor applications. Additionally, poly(neutral red) (PNR) was electrosynthesised by potential cycling on bare glassy carbon and on MWCNT-modified glassy carbon electrodes, and characterised by cyclic voltammetry and scanning electron microscopy. Well-defined voltammetric responses were observed for hexacyanoferrate (II) oxidation with differences between the MWCNT types as well as from loading. The MWCNT and PNR/MWCNT-modified electrodes were applied to the oxidative determination of ascorbate, the electrocatalytic effects observed varying according to the type of nanotubes. Comparison was made with electrodes surface-modified by graphite powder. All modified electrode configurations with and without PNR were successfully employed for ascorbate oxidation at +0.05 V vs saturated calomel electrode with detection limits down to 4 μM; good operational stability and storage stability were also obtained.     

Kinetic Study of the Electro-Catalytic Oxidation of Hydrazine on Cobalt Hydroxide Modified Glassy Carbon Electrode

Electrocatalytic oxidation of hydrazine was investigated on a cobalt hydroxide modified glassy carbon (CHM-GC) electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry techniques as well as steady state polarization measurements. In cyclic voltammetry (CV) studies, in the presence of hydrazine the peak current increase of the oxidation of cobalt hydroxide is followed by a decrease in the corresponding cathodic current. This indicates that hydrazine is oxidized on the redox mediator that is immobilized on the electrode surface via an electrocatalytic mechanism. A mechanism based on the electrochemical generation of Co(IV) active sites and their subsequent consumption by the hydrazine in question was also investigated.     

Electrodeposited nano-scale islands of ruthenium oxide as a bifunctional electrocatalyst for simultaneous catalytic oxidation of hydrazine and hydroxylamine

For the first time, an electrodeposited nano-scale islands of ruthenium oxide (ruthenium oxide nanoparticles), as an excellent bifunctional electrocatalyst, was successfully used for hydrazine and hydroxylamine electrocatalytic oxidation. The results show that, at the present bifunctional modified electrode, two different redox couples of ruthenium oxides serve as electrocatalysts for simultaneous electrocatalytic oxidation of hydrazine and hydroxylamine. At the modified electrode surface, the peaks of differential pulse voltammetry (DPV) for hydrazine and hydroxylamine oxidation were clearly separated from each other when they co-exited in solution. Thus, it was possible to simultaneously determine hydrazine and hydroxylamine in the samples at a ruthenium oxide nanoparticles modified glassy carbon electrode (RuON-GCE). Linear calibration curves were obtained for 2.0-268.3 μM and 268.3-417.3 μM of hydrazine and for 4.0-33.8 μM and 33.8-78.3 μM of hydroxylamine at the modified electrode surface using an amperometric method. The amperometric method also exhibited the detection limits of 0.15 μM and 0.45 μM for hydrazine and hydroxylamine respectively. RuON-GCE was satisfactorily used for determination of spiked hydrazine in two water samples. Moreover, the studied bifunctional modified electrode exhibited high sensitivity, good repeatability, wide linear range and long-term stability.     

Voltammetric sensor for glutathione determination based on ferrocene-modified carbon paste electrode

The electrocatalytic oxidation of glutathione (GSH) has been studied at the surface of ferrocene-modified carbon paste electrode (FMCPE). Cyclic voltammetry (CV), double potential step chronoamperometry, and differential pulse voltammetry (DPV) techniques were used to investigate the suitability of incorporation of ferrocene into FMCPE as a mediator for the electrocatalytic oxidation of GSH in buffered aqueous solution. Results showed that pH 7.00 is the most suitable for this purpose. In the optimum condition (pH 7.00), the electrocatalytic ability of about 480 mV can be found and the heterogeneous rate constant of catalytic reaction was calculated as . Also, the diffusion coefficient of glutathione, D, was found to be 3.61 × 10^–5 cm² s⁻¹. The electrocatalytic oxidation peak current of glutathione at the surface of this modified electrode was linearly dependent on the GSH concentration and the linear analytical curves were obtained in the ranges of 3.2 × 10^–5 M–1.6 × 10^–3 M and 2.2 × 10^–6 M–3.5 × 10^–3 M with cyclic voltammetry and differential pulse voltammetry methods, respectively. The detection limits (3σ) were determined as 1.8 × 10^–5 M and 2.1 × 10^–6 M using CV and DPV, respectively. Finally, the electrocatalytic oxidation of GSH at the surface of this modified electrode can be employed as a new method for the voltammetric determination of glutathione in real samples such as human plasma.     

A nanomaterial composed of cobalt nanoparticles, poly(3,4-ethylenedioxythiophene) and graphene with high electrocatalytic activity for nitrite oxidation

We have investigated the oxidative electrochemistry of nitrite on glassy carbon electrodes modified with cobalt nanoparticles, poly(3,4-ethylenedioxythiophene) (PEDOT), and graphene. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The results suggest that this new type of electrode combines the advantages of PEDOT-graphene films and cobalt nanoparticles and exhibits excellent electrocatalytic activity towards the oxidation of nitrite. There is a linear relationship between the peak current and the nitrite concentration in the range from 0.5?μM to 240?μM, and the detection limit is 0.15?μM. The modified electrodes also enable the determination of nitrite at low potentials where the noise level and interferences by other electro-oxidizable compounds are weak.